That's why we haven't gotten more directly involved in Ukraine, even to the point of not providing weapons to Ukraine, to avoid escalation. Russian attitudes seem far more cavalier, just like Russian bomber flights to try and intimidate the Turks. The Turks -take it from their Allies - can be a pain in the ass and rarely do what they are expected to do.
I'm sure the Turks are secure in the knowledge that if Russia takes its from theories into practice, then NATO will be involved, and I know NATO has contingency plans on how to neutralize Russian bomber bases, see where this is headed? A very slippery slope, so is Assad and worth it?
And again, that would mean war with NATO and the United States. Russia can make military moves, but it's adversaries are not without teeth so the danger is real, fighting NATO won't be like fighting the Ukrainians.
As I understand it, Turkish tubed artillery was used on several occasions after Syyrian indirect fire landed in Turkey, probably not intentional, but I don't think saying that didn't happen would be accurate.
I think if Russia wants to achieve its objectives without starting "the big one", not giving the Turks and excuse would be a start, conducting combat sorties on each others borders carries inherit risk of a wider war, that should be obvious even before this incident, the recent shoot down should only drive that point home.
I don't think anybody wants to be turned into radioactive dust, whether you're Russian, American, European, Chinese, or even Turkish. That's why NATO showed so much restraint during the ColdWar, and even now, though they've expanded a lot. World War Three spells doom for all, and no one wants that.
Ukraine has intricacies that can be largely debated on, due to the fact it's ongoing in many ways.
The problem with Syria is even more complex:
1). ISIS, F.S.A, Syria, SDF/Kurds all share a border with Turkey.
2). A majority of the supply lifeline to terrorist organizations in Syria flows through Turkey(I Don't see any Turkish border guards, or military personnel trying to prevent this).
3) It's a complete Quagmire, with Rebel groups fighting each other, some "Moderate" factions aligning themselves with Extremist groups like Al nusra and Al Qaeda.
4). A lot of these rebel groups are opposed to Kurds as well.
Now, what is one common denominator in all of this?
The Turkish Border.
The Su-24 that was shot down, was carrying out operations against those very supply lines. It's only Logical for Russia, and even Nato for that matter to close off all those supply routes, at the very least for ISIS. Turkey could have there border tight and secure along the ISIS routes, but they haven't. That's why all these convoys are being bombed, no other logical choice for Russia's goals.
